1. Field of the Invention
The invention relates to an inkjet apparatus, and more particularly to a calibration method for an inkjet apparatus.
2. Description of the Related Art
FIG. 1 shows a diagram of a conventional piezoelectric inkjet print head 10. In FIG. 1, the piezoelectric inkjet print head 10 comprises a plurality of nozzles, such as 256 nozzles. An equivalent circuit of each nozzle is shown as a capacitor CL, i.e. a capacitor CL1 represents a 1st nozzle and a capacitor CL256 represents a 256th nozzle. Typically, each nozzle of the piezoelectric inkjet print head is driven by the same driving signal. However, each nozzle has different impedance due to the fluctuations of piezoelectricity thin film processing and different aging of nozzles. Thus, if each nozzle of the inkjet print head is driven by the same driving signal, a portion of the nozzles are unable to drop ink such that efficiency of the inkjet print head 10 is gradually decreased. Additionally, when the same driving signal is used to drive each nozzle, some nozzles will drop defect ink, such as different drop volume or flying speed. With abnormal nozzles sacrificed due to the defect ink, the utility rate of the nozzles is decreased, along with printing speed and printing quality.
U.S. Pat. No. 5,037,217 discloses a printer system for controlling a piezoelectric inkjet print head, wherein the system detects a thickness of a recording medium and ambient temperature to determine a dynamic voltage and a static voltage, respectively. Hence, the piezoelectric inkjet print head operates between the dynamic and static voltages when a print process is performed. Moreover, U.S. Pat. No. 6,286,922 discloses a control system for controlling a driving pulse of a piezoelectric element in an inkjet print head. For the driving pulse, a rising slope and a falling slope of a voltage waveform of the driving pulse are determined by a control signal and a pulse generator. Hence, the control system measures a maximum voltage value of the driving pulse and adjusts the control signal, such that the maximum voltage value of the driving pulse will reach a predetermined voltage value.